Explain how the greenhouse effect keeps the Earth warm enough to support life.

Eduqas GCSE Chemistry — C9 Chemistry of the atmosphere · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Short‑wave solar radiation passes through the atmosphere and reaches the Earth's surface.
The surface absorbs this energy and re‑emits it as longer‑wave (infrared) radiation.
Greenhouse gases in the atmosphere absorb some of this infrared radiation, preventing it from escaping directly into space.
The absorbed energy is then re‑emitted in all directions, including back towards the surface, which keeps the Earth warm enough to support life.

Examiner tips

Use the exact terms ‘short‑wave’, ‘infrared’, ‘greenhouse gases’, and ‘re‑emitted’ to match the mark scheme.
Show the sequence of steps in order – radiation reaches surface, surface emits IR, GHGs absorb, IR is re‑emitted back to Earth.
Mention that the back‑radiation raises/maintains temperature to earn full marks.

Common mistakes

Confusing short‑wave with long‑wave radiation; students sometimes say the Sun emits infrared. Omitting the step that greenhouse gases absorb the IR. Using vague phrases like ‘heat the Earth’ instead of ‘re‑emit back to the surface’.

Mark scheme (4 marks)

Short-wave/solar radiation from the Sun passes through the atmosphere and reaches the Earth's surface
The Earth's surface absorbs this radiation and re-emits it as longer-wave/infrared radiation
Greenhouse gases in the atmosphere absorb this infrared radiation (preventing it from escaping into space)
The absorbed energy is re-emitted in all directions, including back towards Earth, raising/maintaining the Earth's temperature

Key terms in this question

greenhouse effect